Method and apparatus for uniformly heating intermittently moving metallic material



Nov- 1, 1 o. M. MARQUARDT 2,722,589

METHOD AND APPARATUS FOR UNIFORMLY HEATING INTERMITTENTLY MOVINGMETALLIC MATERIAL Filed Nov. 50, 1950 2 Sheets-Sheet 1 INVENTOR. G770MMAAQUA R0 7' Nov, 1, 1955 o. M. MARQUARDT 2,722,589

METHOD AND APPARATUS FOR UNIFORMLY HEATING INTERMITTENTLY MOVINGMETALLIC MATERIAL Filed Nov. 30, 1950 2 Sheets-Sheet 2 I N V EN TOR.0270 M. NAFQUARQT raEy United States Patent Otto M. Marquardt, Solon,Ohio, assignor to The Ohio Crankshaft Company, Cleveland, Ohio, acorporation of Ohio Application November 30, 1950, Serial No. 198,459

6 Claims. (Cl. 219--10.61)

This invention pertains to the art of high-frequency induction heatingand, more particularly, to a method and apparatus for uniformly heating,by a heater that has an inherent nonuniform heating pattern, a portionof an elongated member which must be intermittently advanced past theheater.

The invention is particularly adaptable to heating to aforgingtemperature an end portion of a metallic strip, which end, when heated,must be advanced at spaced intervals into a punch or forge and, for theforging operation, must be heated uniformly over its entire length.

In the art of high-frequency induction heating, it has been quitedifiicult in the past to uniformly heat metallic articles of certainconventional cross-sectional shapes. One of these shapes has been flatmetallic strip. With fiat strip, the tendency is for either the centerof the strip to heat or for the edges of the strip to heat and thistendency may shift in the course of heating as the temperature of thestrip passes through the Curie-point temperature. This shift of heatpattern is particularly true where the high-frequency inductor is in theform of a helix with the strip passing axially through the helix.Composite inductors have been providecl, one part of which is adapted toheat the edges and the other part of which is adapted to heat thecenter. The heating of edges and center cannot take place at theidentical points of the strip and, therefore, i v

a uniform continuous movement of the strip has been required if uniformheating is to be obtained.

Transverse flux inductors have been employed for the heating of strip.Such inductors take their name from the fact that the flux is forceddirectly through the strip from the core of one inductor to the core ofa second inductor. Such inductors, however, tend to heat narrowtransverse bands on the strip. Therefore, in order to obtain uniformheating, the strip must be moving forward relative to the inductor at auniform rate. Also, the inductor should have a strip positioned thereinover substantially its entire length for proper electrical loading.Another problem with high-frequency induction heating of strip to be fedinto forges and the like has been that the inductor itself must bespaced from the press. This is to allow clearance for the dies of thepress and, also, to prevent stray flux fields from causing undesirablecirculatory currents in the metal of the press. On the other hand, it isimpossible to let the heated piece hang free between the inductor andthe punch press due to the rapid cooling of the piece at the elevatedtemperatures and sagging due to its weight. This cooling on thin stripcan be as high as 100 degrees per second.

The present invention attempts to make use of transverse-type inductionheaters for uniformly heating a periodically or intermittently moving oradvancing workpiece such as strip or bar or wire. For the purposes ofconvenience, the workpiece upon which the present invention is operablewill be termed generally strip.

In accordance with the present invention, the portion of the strip to beheated and the inductor are moved in an oscillatory or reciprocatorymanner continuously relative to each other during the heating cycle sothat, to all intents and purposes, the inductor sees the strip as thoughit was progressively moving relative thereto. The amount ofreciprocation of the inductor, if transverse flux inductors areemployed, is such as to at least span the distance between the narrowportions which would heat it the relative movement were not employed.When the portion to be forged has reached the desired temperature, it isadvanced to the punch or forge, cut off and the strip is then retractedto bring the remaining portion of the strip back into the inductor. Insome instances, the radiation and temperature loss of the strip due toits advancing from the inductor to the punch may be excessive. In thisevent, the entire inductor which forms a radiation-preventing housingfor the strip may be advanced as far as possible toward the press alongwith the strip to prevent the temperature losses of the strip.

In view of the above, it is an object of the present invention toprovide a new and improved method for uniformly heating, using aninductor having a relative nonuniform heat pattern, a portion of ametallic strip which is advancing intermittently through the inductor,which method comprises oscillating the inductor and strip relative toeach other during the heating operation; and, when the heating operationis completed, advancing the strip rapidly through the inductor to whereit is to be used. 7

Another object is the provision of a new and improved method of the typereferred to wherein the strip and inductor are moved continuouslyrelative to each other until the desired portion of the strip is heatedto the tie sired temperature. The strip and inductor are then advancedin the same direction but the strip to a greater distance than theinductor so that the inductor may prevent radiation from the strip for aportion of its travel from furnace to forge or press.

Still another object of the invention is the provision of a new andimproved apparatus for uniformly heating the portions of intermittentlyadvancing metallic strip cornrocating the inductor relative to the stripduring the heating operation.

Still another object is the provision of apparatus of the type referredto wherein the inductor and the means for reciprocating the inductorrelative to the strip are, in turn, mounted for reciprocation in adirection longitudinally of the strip. 7

The invention may be embodied in practical form in a number of diiterentphysical arrangements of parts and inductors. For the purposes of betterillustrating the invention, a single preferred embodiment will bedescribed in this specification and. illustrated in the attached drawingwhich is apart hereof, and wherein:

Figure l is a side view, partly broken away, showing apparatusconstructed in accordance with the present invention and which iscapable of carrying out the method of the present invention;

Figure 2 is a sectional view on the line 22 of Figure l; and

Figure 3 is a fragmentary sectional view taken approximately on the line3-3 of Figure 2.

Referring now to the drawings wherein the showing is for the purposes ofillustrating the invention only, the figures show a fiat metallic stripA being intermittently advanced from right to left into a forge press Bby a feeder mechanism C and with a high-frequency induction heating unitD disposed intermediate the feeder and the forge for the purpose ofheating the strip to a forging temperature.

The flat metallic strip A shown may be of steel or other material ofeither high or low carbon or alloy. Other cross-sectional shapes couldalso be employed. This strip is generally a continuous length fed from acoil (not shown) if it is of such a small thickness that it can becoiled, or from an ordinary rack if it is such a thickness that itcannot be coiled. It is preferred that if strip is fed from a roll, thefeeder mechanism be preceded by a welding unit so that the tail end ofone coil of strip may be welded to the leading end of another coil ofstrip so that there will be continuous lengths of strip fed to theforge.

The forge is more or less conventional and forms no part of the presentinvention but may include a pair of mating dies which are adapted to beforcefully closed on the heated portion of the strip to suitably shapeit. The forge may also include a cut off for the strip, which cut offwill generally precede the forging operation. In operation, the strip Athen is advanced intermittently into the forge, cut off and thenforcefully shaped to the desired configuration.

The strip is advanced by the feeder mechanism C which again forms nopart of the present invention and may be of any conventionalconstruction. As shown, it is spaced a substantial distance from theforge B. p The induction-heating unit D includes a pair of generallyidentical high-frequency inductor assemblies 10, 11 mounted in spaced,parallel relationship on opposite sides of the strip A. As theassemblies are identical in construction, only the assembly will bedescribed in detail and like numerals will be used to designate likeparts in the assembly 11.

The inductor assembly 10 is comprised of three (there may be more orless) identical aligned inductor elements 12, 13 and 14. Each inductorelement 12, 13, 14 is comprised of a stack of thin,magnetically-permeable laminations 15 having the plane thereofperpendicular to the plane of the strip and parallel to the line ofmovement thereof. The magnetically-permeable laminations 15 areinterleaved by three cooling laminations 21 formed of a material of highheat conductivity, such as copper. The stripadjacent side of each stackof laminations has a pair of transverse slots in which a two-turnwinding of an electrical conductor 16 is disposed. Each turn of theconductor, as shown, is insulated from the other and from thelaminations by insulation 29. An insulating-retainer strip 9 extendsacross and closes the lower end of the transverse slot to retain thewinding therein. This strip 9 may be retained in position by anysuitable means but is shown as having its edges extending into groovesin the walls of the slots. While a two-turn winding is shown, obviouslymore or less turns could be employed. The windings of each inductorelement can be connected in electrical parallel relationship with eachother; but, preferably, they are connected in electrical seriesrelationship so that the direction of the current in each slot from oneend of the inductor unit to the other will alternate as shown by theplus and minus signs in Figure l. The arrangement is shown more clearlyin Figure 3. As stated, the inductor assembly 11 is generally identicalin construction to the inductor assembly 10 and the slots in thelaminations of the inductor assembly 11 are preferably disposed directlyopposite the slots of the laminations of the inductor elements 12, 13and 14. The direction of the current in the windings of the inductorassembly 11 are in the same direction as that of the winding of theinductor assembly 10. The effect is that the flux caused by current flowin the conductors will flow transversely through the strip A andgenerate high-frequency, highdensity, electric currents to flow in thestrip A.

The inductor assembly 10 is fastened to an upper supporting plate 17formed of an electrically-conductive a ti heat-conductive material suchas copper. The cooling laminations 21 are brazed to this plate toprovide effective heat transfer to the plate. The inductor assembly 11,in a like manner, is fastened to a lower supporting plate 18 of likematerial.

Both plates 17 and 18 have copper tubes 20 brazed to the outer surfacesthereof. Cooling water may be circulated through the tubes 20 to removeany heat which may be generated in the laminations 15 and conducted tothe plates 17, 18 through the cooling laminations 21.

The plates 17, 18 are held in fixed, spaced relationship by a pair ofside members 19 preferably formed of an electrically-insulatingmaterial. Screws are shown as holding the members 17, 18 and 19 inassembled relationship. The length of the members 19 controls thespacing between the inductor assemblies 10, 11 and, therefore, theclearance between the strip A and the strip-facing surfaces of theinductor assemblies.

As shown, the ends of the legs of the laminations are spaced and thestrip A extends through this space.

With apparatus of this type, difiiculty is sometimes ex perienced withthe magnetic field pulling the metallic strip, if it is of a magneticmaterial, into actual physical engagement with the laminations. This isundesirable. Also, it is necessary, with the construction of the typedescribed, that the strip itself be accurately aligned relative to theinductor. In the embodiment shown, guides 22 extend the length of theinductor in the space between the two inductors and have a channel 23formed on their facing surfaces into which the edges of the strip A mayextend and be guided thereby. It is preferred that these guides beformed of a nonmagnetic material in order that the amount of heating byhysteresis in the guides may be held down to a minimum. The guides maytake a number of different forms of construction but, in the embodimentshown, they are made up of a number of flat steel strips welded orbrazed together about a hollow copper tube 24 to form a channel member.Water may be circulated through the tube 24 for the purposes of coolingthe guides.

Referring now specifically to Figure 3, it will be noted that thethickness of the stack of laminations is considerably less than thewidth of the strip A while, at the same time, the conductor 16, informing the winding between one transverse slot and the other, extendsbeyond the edges of the strip A. With such a construction, the evennessof the heat pattern may be accurately controlled by increasing ordecreasing the thickness of the stack of laminations. Thus, if the striptends to heat too much in the center, the thickness of the stack oflaminations may be increased. If the edges tend to heat too much, thethickness of the stack of laminations may be decreased. It has beenfound that the guides have little effect on the heating of the edges.They are non-magnetic and they have a relatively small transverse widthcompared with the width of the strip.

The heating unit D shown also includes what may be termed a preheatingunit in the form of a helical inducing coil 31. This coil 31 ispositioned at the end of the unit D adjacent the strip feeder C and issupported in position by a pair of spaced arms 40, 41 fixed to themember 19. The coil 31 preferably has an axial crosssectional shapewhich is substantially rectangular and the strip A passes through thiscoil before entering the space between the inductor assemblies 10, 11.The coil 31 may be connected electrically in series or in parallel withthe coils of the inductors 10, 11 or it may be separately energized asshown. The coil 31 has the characteristic, with thin strip, that if thestrip is allowed to remain stationary in the coil, the strip will heatto the Curie point and not beyond, regardless of the amount of powersupplied to the coil or the length of time that the strip remainstherein.

The use of such a coil greatly contributes to obtaining an increaseduniformity of final temperature of the strip as it emerges from theinductiomheating unit to be forged into the heating unit- D. The 'coil31 is capable of heating the entirestrip entirely across its widthuniformly to the sametemperature at or near the Curie point. Thus, theinductors 10, ll'necd only raise the temperature from the Curie point tothe forging temperature and it'has been found that a far greateruniformity of temperature over the entire width of the strip can beobtained.

In the embodiment shown, the conductors 16 of one inductor are disposedopposite the conductors 16 of the other inductor. Correspondingconductors 16 of each inductor have the current flowing therein in thesame direction such that the flux in the laminations will tend to passdirectly from one stack of laminations to the other; that is to say,transversely through the strip A. Normally, with such a construction,heating of the strip, assuming that the strip is not moving continuouslyin one direction relative to the inductor, as is usually the case, willoccur between the opposed conductors 16 and transversely across thestrip and along the edges intermediate the transverse heated portions.Obviously, with such an arrangement, it would be impossible to obtain auniformly heated length of strip which is so necessary for forgingoperations; and, yet, in the particular field to which this inventionapplies, the strip cannot be continuously progressively moved relativeto the inductor because of the intermittent use of heated strip by theforge B.

In accordance with the present invention, the inductionheating unit iscontinuously moved relative to the strip even though the strip may berelatively stationary to an observer. Thus, the inductor unit D iscontinuously moved or reciprocated in a direction parallel to theiongitudinal length of the strip A and, accordingly, theinduction-heating unit D is suitably supported on a rack 30 for suchmovement. In the embodiment shown, the rack has longitudinally extendingways and the housing has correspondingly shaped surfaces to slide in theways.

Suitable means are provided for the purpose of oscillating orreciprocating the induction-heating unit D. In the embodiment shown, acrank and connecting rod arrangement are shown consisting of aconnecting rod 33 pivoted at one end to a lug 34 fastened to the bottomside of the induction-heating unit and at the other end pivoted on acrank pin 34 of a crank member 32 which, in this instance, is a diskrotated about an axis by a motor M through a variable-speed mechanism(not shown). As shown, the crank pin 34 may be mounted in a threadedopening 35 on the disk and a plurality of such openings are providedlocated at varied distances from the axis of rotation of the disk sothat the amount of movement of the induction-heating unit D may becontrolled. Other types of mechanism may be employed for reciprocatingthe unit D.

In the heating of thin metallic strip, the heat radiation which occursat forging temperatures is very rapid. Obviously, there must be somespace between the exit end of the inductor unit'D and the forge B evenwhen the inductor unit is advanced the maximum amount toward the forgeunit B. With a normal and conventional intermittent advancement of thestrip A by the strip feeder C, it will be appreciated that there wouldalways be a free end of the strip A projecting beyond the end of theinductor unit D and, in the time required between the feed movements,this projecting end would cool to an extent which cannot be tolerated ifthe strip is to be at the maximum temper t re when it enters the forgingdie. The inventi n, c rdingly, contemplates that th strip feeder C willadvance the strip A into the forge the required distance and, when theend of the strip has been cut off of a cut-off mechanism in the forge B,the strip feeder mechanism will then act to draw the free end of thestrip A back into the inductor unit D where the heating of the entireend of the strip may be continued so that, when the strip is againadvanced; the entire end of it which is to go into the forge B- will beat the maximum and desired forging temperature.

A preferred embodiment of the invention has been described in order tomore fully explain the aspects of the invention. It would be appreciatedthat other embodiments will also come within the scope of the invention.For example, but without limitation, the transverse slots of thelaminations could extend longitudinally of the strip and the inductorassembly could be oscillated transversely to the length of the strip andthen, when it is time to feed a strip to the forge, the entireinductionheating unit B could be oscillated in a longitudinal direction.

It would be appreciated that other modifications will occur to thoseskilled in the art upon a reading and understanding of thisspecification. It is my intention to include such modifications andalterations even though they differ radically in appearance from thedescribed preferred embodiment so long as such modifications andalterations come within the scope of the appended claims.

Having thus described by invention, 1 claim: i

l. The method of uniformly heating intermittently moving metallic stripwith a heater unit which inherently has a nonuniform heating patternwhich comprises advancing said strip intermittently through said heatingunit and simultaneously and continuously oscillating said heating unitrelative to said strip in the plane of movement thereof and out of phasewith the intermittent advancing of said strip.

2. The method of uniformly heating predetermined lengths ofintermittently advancing metallic strip material with a heating unitwhich has an inherently nonuniform heating pattern which comprisesintermittently advancing said strip and continuously oscillating saidheating unit relative to said strip in the plane of movement thereof andout of phase with the intermittent advancing of said strip.

3. The method of uniformly heating predetermined lengths ofintermittently advancing metallic strip material with a high-frequencytransverse flux-type heating unit which tends to heat a plurality ofgenerally rectangular patterns on said strip which comprisesintermittently advancing said strip and continuously oscillating saidunit relative to said strip in the plane of movement thereof a distanceat least equal to the distance between the side of said rectangularheating pattern.

4. The method of claim 3 wherein the strip is magnetic and is firstheated to the Curie point before being subjected to the heating actionof the transverse flux unit.

5. Apparatus for uniformly heating intermittently moving metallic stripwith a heater unit which inherently has a nonuniform heating patterncomprising, in combination, a high-frequency induction-heating unit ofthe transverse flux type, means for intermittently feeding an elongatedworkpiece past said heating unit at predetermined intervals and othermeans for continuously reciprocating the heating unit along the line ofmovement of said workpiece and out of phase with the intermittentfeeding of said workpiece whereby to provide uniformly heated lengths ofstrip material.

6. Apparatus for uniformly heating predetermined lengths ofintermittently advancing metallic strip material with a heating unitwhich has an inherently nonuniform heating pattern comprising, incombination, a heating unit comprised of high-frequency inductorspositioned in close-spaced relationship to the workpiece and lying inthe general plane of the surface of said workpiece, means forintermittently advancing said workpiece along the line of movement pastsaid inductor and other means for reciprocating the heating unit in theplane of said strip out of phase with such intermittent advancingthereof whereby to uniformly heat the strip to an elevated temperature.

(References on following page) References Cited in the file of thispatent UNITED STATES PATENTS Northrup May 30, 1933 Denneen et a1 May 28,1940 5 Kersting Feb. 24, 1942 Patterson Aug. 10, 1943 '8 Bierwirth eta1. June Denneen et a1. Jan. Rohdin May .Baker et al. Aug. Crowe Aug.Crowe Jan. Detuno et a1. Apr.

1. THE METHOD OF UNIFORMLY HEATING INTERMITTENTLY MOVING METALLIC STRIPWITH A HEATER UNIT WHICH INHERENTLY HAS A NONUNIFORM HEATING PATTERNWHICH COMPRISES ADVANCING SAID STRIP INTEMITTENTLY THROUGH SAID HEATINGUNIT AND SIMULTANEOUSLY AND CONTINUOUSLY OSCILLATING SAID HEATING UNITRELATIVE TO SAID STRIP IN THE PLANE OF MOVEMENT THEREOF AND OUT OF PHASEWITH THE INTERMITTENT ADVANCING OF SAID STRIP.